Energy harvesting is a process by which energy is captured from external, or environmental, sources. For example, solar power and wind energy are two common energy harvesting schemes. Many other schemes exist with varying success, including thermal energy, kinetic energy, salinity gradients, and electromagnetic (EM) fields. Environmental energy sources typically yield small amounts of power that are well suited for low-energy applications.
Many low-energy applications have non-continuous and, in some cases, periodic power demands. For example, wireless sensor networks can have tens, hundreds, or even thousands of wireless sensor nodes, each of which operates relatively infrequently, as opposed to continuous draw applications. An individual sensor node may update once every hour, or once every minute. In any case, the time period between activities allows the energy harvesting scheme to accumulate sufficient power to operate the sensor node. While energy harvesting is generally a scalable technology, it assumes a minor role in large-scale, continuous draw applications, where battery power and “grid” power dominate.